Sedimentary Facies PDF

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Sedimentary Facies Prof. Mohamed Fouad Aly Concept of Sedimentary Facies Sedimentary Facies • Refers to all of the characteristics of a particular rock unit. • The characteristics of the rock unit come from the depositional environment. Facies A body of sedimentary rock distinguished from others by ...

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Sedimentary Facies Eslam Gamal

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Sedimentary Facies Prof. Mohamed Fouad Aly

Concept of Sedimentary Facies

Sedimentary Facies • Refers to all of the characteristics of a particular rock unit. • The characteristics of the rock unit come from the depositional environment.

Facies A body of sedimentary rock distinguished from others by its lithology, geometry, sedimentary structures, proximity to other types of sedimentary rock, and fossil content, and recognized as characteristic of a particular depositional environment.

Facies Sedimentary facies are bodies of sediment recognizably different from adjacent sediment deposited in a different depositional environment.

Facies The character of a rock expressed by its formation, composition, and fossil content.

Facies • All the properties of a body of rock that allow us to differentiate it

from those above, below or laterally adjacent to it. • Properties include • • • • •

• • • •

Lithology – rock type, including color, etc. Composition – mineral content Texture – grain size, sorting, roundness Sedimentary structures Fossils

Facies means aspect – same Latin root as “face” Overall appearance of a rock body Facies are the products of depositional environments Examples: • • • •

Planar laminated fine quartz arenite facies Bioturbated, poorly sorted muddy skeletal limestone facies Cross-stratified arkosic conglomerate facies Stromatoporoid-tabulate coral reef facies

Facies Model Facies models are intellectual aids to the understanding of sedimentary environments and the origin of ancient sedimentary rocks. An idealized description of a facies Constructed from modern environments and ancient rocks Serves as a Norm for comparison Framework for observation Predictor of patterns

Facies Patterns Groups of facies commonly show patterns Proximal Facies (near the source) tend to be coarse grained, reflecting high energy regime. Distal Facies (far from source) tend to be finer grained, reflecting low energy regime. This pattern is displayed upstream and down in rivers and onshore to offshore in coastal areas Facies are arranged according to distribution of depositional environments

Facies Migration Facies migrate through space and time Migration is in response to environmental factors Sediment supply Sea level change Subsidence

Facies become stacked during migration A single facies is likely to be different ages in different locations

Walther’s Law “a vertical sequence of facies will be the product of a series of depositional environments which lay laterally adjacent to each other”

Johannes Walther (1860-1937)

Walther’s Law of the Correlation of Facies Only works where there are no unconformities. Only facies that were laterally adjacent during deposition (result of laterally adjacent environments) can be stacked vertically, Vertical arrangement of facies gives us information on: Distribution of environments How environments migrated through space and time

Used as a basis to build facies maps or paleogeographic maps. Accurate time correlation of facies is essential. Time lines provide framework for correlation Bio-events Volcanic ashes Other thin, unique lithologies or marker beds

Marine Transgression = Sea Level Rise Marine Regression = Sea Level Fall

Walther’s Law Sedimentary environments that started out side-by-side will end up overlapping one another over time due to transgressions and regressions.

Facies Limestone

Reef

Shale

Siltstone

Lagoon Near Shore Environment

Sandstone

Beach

Marine Transgression

Walther’s Law

Marine Regression

Way-up indicators in sedimentary rocks “a characteristic relationship observed in a sedimentary or volcanic rock, or sequence of rocks, that makes it possible to determine whether they are the right way up (i.e. in the attitude in which they were originally deposited, also known as "stratigraphic up") or have been overturned by subsequent deformation”

Lithostratigraphy Each layer is a different rock type.

Chronostratigraphy Each layer is a different age.

Biostratigraphy Each layer contains a different fossil assemblage.

Lithostratigraphic Units Member A Formation A

Member B Member C

Group A

Member D Formation B

Member E Member F

Formation C

Member G Member H Member I Member J

Supergroup

Formation D

Member K Member L Member M Member N

Group B Formation E

Member O Member P Member Q Member R

Formation F

Member S Member T

Supergroup | Group |

Formation | Member | Bed

Lithostratigraphic Example: Grand Canyon

Stratigraphic Column: John Day Fossil Beds NM

Geologic Maps Snoqualmie Pass

Chronostratigraphic Map of Washington

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